While many of saccharide derivatives are important as physiologically active substances, it is not easy to prepare them by synthetic means. Saccharides contain a plurality of hydroxyl groups as functional groups in the molecules. Generally, upon reacting a reagent with a saccharide, various reaction products having substituents at different sites are produced simultaneously as by-products, and the efficiency of obtaining a desired product is very low. In synthesizing derivatives from corresponding saccharides, processes via derivatives in which hydroxyl groups are converted into ester groups or ether groups have been employed. Among them, acetylation is particularly useful since relatively moderate conditions can be applied as the reaction conditions, and the reaction products are generally solvent-soluble. However, when an acetyl derivative is subjected to hydrolysis, the selectivity with respect to the position of the ester bonds to be hydrolyzed is poor, resulting in a plurality of products of different structures.
For the reasons as described above, in synthesizing a saccharide derivative having a desired structure, it is necessary, in addition to the reaction with a predetermined reagent, to repeat the steps of introducing protective groups to protect hydroxyl groups, then removing the protective groups, and separating and purifying the product. This necessiates long series of steps and renders it difficult to obtain a desired derivative in a high yield.
Accordingly, although it is very much desired from a practical point of view to discover a process capable of preparing, effectively and in a short series of steps, a monosaccharide or oligosaccharide having hydroxyl groups that can be reacted with oxygen atoms only on carbon atoms at specific positions, while other hydroxyl groups being protected by substituents, no practicable process has yet been found.